Would someone be able to fill me on in what is required with regard to bank accounts in the state of NC for holding a tenant's security deposit? 

Handling Maintenance requests and emergencies, Handling tenant disputes, Ensuring the tenants are properly insured (if you require them to), Marketing the property, Screening applicants, Handling the security deposit return, and a whole lot more. 

It sounds like at least some of the charges to your security deposit might be valid. 

Ideally, a location near a hospital or other attractive amenities is ideal.The upfront investment you would need is the Security deposit and 1st months rent, and cash to furnish the unit.

It’s often sold as an alternative to larger security deposits or co-signers for people with bad credit bad rental history.

If you do get contacted by someone who is serious (with experience) then just request a large deposit to protect yourself. 

Florida for example, many landlords I speak to don't understand Security Deposits. 

For extra formality, put it on a nice document with your letterhead.Re: Non-Binding Letter of Intent to Purchase Real Property Located at [Property Address]Dear [Recipient's Name]:This non-binding Letter of Intent ("LOI") is submitted by [Your Name] (the "Buyer") to [Recipient's Name] (the "Seller") with the intention of setting forth certain preliminary terms and conditions for the proposed acquisition of the real property located at [Property Address], inclusive of all improvements, appurtenances, and fixtures thereon (the "Property").Purchase PriceThe Buyer hereby proposes to purchase the Property for a total consideration of $[Amount] (the "Purchase Price"), which shall be subject to adjustment based on the results of the due diligence investigations and final negotiations.Earnest Money DepositContingent upon the execution of a definitive Purchase and Sale Agreement (the "PSA"), the Buyer shall deposit earnest money in the amount of $[Amount] (the "Earnest Money") into an escrow account designated by the mutual agreement of the parties.

About once every year or two I get the “what if the $20k in rent deposit never happens?”

We would NOT need to order a 1007 market rent report if we had either:1st months rent and security deposit2 months of rent deposits (canceled checks)If it’s a departing residence we could only use rental income to offset monthly payment (we couldn’t use extra income if 75% of the lease was 3,000 and mortgage was only $2,500 I couldn’t give $500 of income to boost DTI unless he has moved out of the home for some time and we have 1 year of history of being a landlord (which it sounds like we do, just not sure if he’s just moving out of this home).